1. Field of the Invention
The present invention relates to circuit for adaptively selecting three-dimensional sub-band signals of an image signal in an image processing system. More particularly, the present invention relates to a circuit for adaptively selecting three-dimensional sub-band signals of the image signal, which obtains the energy of each band of three-dimensional sub-band signals, extracts sub-band information on the basis of the activity of the higher frequency sub-band signals, selects predetermined ones of the sub-band signals to be transferred from a look-up table in accordance with the extracted information, and restores the original image by using the selected sub-band signals and sub-band information. A method for adaptively selecting three-dimensional sub-band image signal in an image processing system is also disclosed.
2. Description of the Prior Art
With improved techniques for processing digital signals and with advanced techniques for manufacturing elements, such as a semiconductor device embodying such digital signal processing techniques, it is now possible to preferentially digitally transfer the higher frequency image signal components. One method for transferring the image signal is the well known sub-band coding method which divides the image signal into several sub-bands, quantizes the sub-bands on the basis of their signal levels and transfers the quantized sub-band signals. In the sub-band coding method, the lower frequency signal area contains a large amounts of energy while the higher frequency signal area contains a relatively small amount of energy. For this reason, a large number of coding bits are assigned to the lower frequency sub-bands having the high energy while a small number of coding bits are assigned to the higher frequency sub-bands. Theoretically, this should result in a satisfactory coding operation. However, it will be noted that the fine details of an image signal are generally defined over the higher frequency sub-bands.
U.S. Pat. No 4,943,855 entitled "PROGRESSIVE SUB-BAND IMAGE CODING SYSTEM" discloses an image encoder comprising a filter bank for extracting a plurality of sub-band image signals from an input image signal, a coding circuit for encoding the sub-band image signal arbitrarily selected from the sub-band signals so as to remove surplus data contained in the extracted sub-band signal and a preview device for receiving the remaining signals of the sub-band image signals, excluding the extracted sub-band image signal and the signal output from the coding circuit, and for producing a preliminary signal corresponding the remaining sub-band image signals.
In the device constructed according to U.S. Pat. No. 4,943,855, the process of dividing the input image signal into the sub-band image signals and encoding any one of the sub-band image signals using other sub-band signals is repeatedly effected to encode the image signal. More particularly, the circuit divides the sub-band signal having the maximum energy by a secondary sub-band signal and encodes the other sub-band signals having large amounts of energy with respect to other secondary sub-band signals. As a result, the input image signal can be effectively transferred.
According to the conventional image processing system as previously described, the image signal is divided into sub-band signals and the sub-band signals are quantized on the basis of their signal levels so that the quantized sub-band signals can be desirably transferred. In the conventional method, however, when the number of the sub-band signals is increased, the method can not be adopted effectively for processing the increased number of sub-band signals.